Don't take me wrong. Hand pumping does not get me winded or anything like that. I just feel light on my feet during the high pressure stage of the last couple/three inches of the stroke. It feels a little "unbalanced", that's all.
I understand. As I said, it could very well be your pump. When you get up close to 4500psi, yes, the last few inches can be tough, but you have to remember technique (using your weight and not your muscle).
Also, something I learned the hard way is to NOT try and pump fast with a hand pump!!!
Slow deliberate strokes with enough time at the top of the stroke to allow maximum air input and cooling, AND MOST IMPORTANT... don't hand pump for long sessions (or fast).
Heat is the enemy, so sessions of no more than 40-60 pumps (for me that is 30+/-) before letting the pump rest/cool off and if you have at least 2 hand pumps, you can just keep switching between them to keep going. As long as you don't overheat the pump, it doesn't take long to cool and will last.
Something else I do even though my pumping sessions are short. After I open the relief valve, I slowly pump to take in cooler air and aid in cooling the pump and O-rings.
After I do that a few times, I close the relief valve and slowly pump a few more times to help push any moisture out of the fill line.
If you only have one pump, I would do this while waiting for the pump to cool for the next session. I think it aids in cooling by taking in cooler air and releasing it while not actually compressing it which is what builds up the heat. JMHO
p.s.p.s.
When I say don't pump fast, I mean don't pump too many strokes in a given amount of time. However, as you get to pressures nearing 4500psi, yes, the downstroke needs to be fast/hard enough to make it all the way down. The upstroke should still be slow enough to allow time for air to enter and cool, but the downstroke can/should be fast enough to make the pump go all the way down. Again, technique, technique, technique. Straighten/lock your arms and let your body weight do the work. For lighter folks, an even faster downstroke may/will be required.
